Japan's prime minister says that he will not allow the US military to fly its newest transport aircraft in his country until safety concerns are first addressed.
Yoshihiko Noda told parliament on Tuesday that no flights of the MV-22 Osprey aircraft would be allowed to take place until investigations into two recent crashes were completed.
The crashes took place in April and June, and Japan says that it will not allow them to operate over its airspace and from its soil until the government is satisfied that safety checks have been completed.
The deployment of the MV-22s to a US military base on the island of Okinawa has become a political headache for the Japanese government due to intense local opposition.
Okinawa hosts more than half of the roughly 50,000 US troops in Japan. The deployment of the aircraft has become an issue for anti-US protesters to rally around.
The first 12 Ospreys headed for Okinawa arrived in Japan on Monday.
The Osprey is a hybrid aircraft with rotors that allow it to take off like a helicopter and engines that can tilt forward, enabling it to fly like an airplane at higher speed than helicopters.
The aircraft's development was plagued with issues in its early years in the 1990s, but US officials say the technical glitches have been cleared up.
It is used by the US marines, primarily as a troop transport aircraft, allowing soldiers on the ground greater range than current transport helicopters offer.